How to stop grass growing in my raised beds?

FADiverAugust 5, 2011

Long time veggie eater, first time gardener. I have three raised beds which I plopped right on top of the sod, assuming that ten inches of soil would just smother the grass.

Now that you're all done laughing, I'll continue.

My various vegetables have done pretty good, but as you can imagine, it's been a battle all summer against the grass, especially as the roots are soooo deep. So, thinking about next year, how can I kill this grass? Would laying cardboard over the beds and then putting soil over the cardboard work? Should I get a bunch of that weed barrier cloth? Am I going to have to simply dig them up and pull up the grass roots by hand? Any ideas are greatly appreciated.

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dan_staley(5b/SS 2b AHS 6-7)

Where do you live, what kind of grass, etc.


    Bookmark   August 5, 2011 at 10:34AM
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At the risk of again rousing the anti-chemical purists, there is an effective product called Grass B Gone. Once your vegetables are out of the beds for the season would be a good time to apply this.

    Bookmark   August 5, 2011 at 11:07AM
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Is there a border to the beds--meaning is the grass coming in from the sides as well as from below?
That is surprising that 10 inches did not do it. Is there a lot of grass?--like more than you can reasonably pull, because maybe with time you can conquer it this way. If not, I think your best bet is to remove the soil, pull up roots (as much as you can), lay down cardboard or several sheets of newspaper, and replace the soil.
When I created my raised beds, I dug the sod AND put down cardboard, and I have very few weeds to deal with.

    Bookmark   August 5, 2011 at 12:07PM
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Pull what you can and mulch, or deal with it this season and mulch thicker next season. Try to put down at least 2-4" of mulch...3-4" is better for people who have long/warm summers.

Avoid using hardwood mulches if you plan to keep the beds for many years because they can harbor pest and the wood chunks work their way down into the soil where they are very hard to decompose. Straw (not hay because of seed heads) is a great mulch if it happens to be cheap in your area.

    Bookmark   August 5, 2011 at 12:46PM
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Thanks, everyone. I live in northern Alabama (zone 7b), and the grass is bermuda, and it is coming in from below and the sides. It has really long runners. I've been mulching as well with straw throughout the summer (after first mulching with pine bark last spring and then reading on this board not to do so).

I think I will just dig down and pull up roots as I go. As I stated earlier, it did not seem to seriously affect the plants.

    Bookmark   August 5, 2011 at 1:55PM
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I had the same problem. I put down a lot of newspaper and cardboard and then about 8 inches of growing mix. Within a week the grass had started growing up through it. I couldn't believe it, but as they came up I just pulled it out. Now in my second year the grass has finally stopped. I did dig up all around my boxes and put down weedcloth and mulch as well, so that stopped the grass from growing up the sides.

I won't make this mistake again, though!

    Bookmark   August 5, 2011 at 2:17PM
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dan_staley(5b/SS 2b AHS 6-7)

Yes, of course. Bermuda is a different animal. You'll have to pull the beds out. Kill all the runners. Then spray to a foot minimum beyond beds. Continue often as it will return. And return. And return. And return. And... Do not underestimate what it can do.

OT but related: in undergrad, a classmate of mine wrote a term paper on Bermudagrass, chock full of facts and anecdotes. The plant is an amazing survivor and incredible what it can do. I have lots of stories from the old landscape business.


    Bookmark   August 5, 2011 at 2:31PM
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Have you carefully followed some of the grass down to verify that it is indeed coming from the original sod? I have a few raised beds and there were some grass/weed seeds in the dirt I filled with. A few weeks later I saw blades of grass coming up from pretty deep down, but none were coming up from the bottom.

Here in KY we usualy have bluegrass or fescue and its easily killed off with 3+ inches of soil or even grass clippings. Ive had grass die just from not raking some thick layers after mowing. But Ive no experience with bermuda so...

    Bookmark   August 5, 2011 at 2:35PM
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Tiffany, purpleinopp GardenWeb, Z8b Opp, AL

FADiver, You could put a cardboard border around the bed. Bermuda is incredibly tenacious grass, I have it, too. I'm going to use 12" pavers as a solid border around my beds. Probably with cardboard underneath to make sure nothing stays alive in the cracks. I'd never seen grass that would grow straight up a wall until I moved here.

A thick layer of oak leaves will kill bermuda grass. If you have oak trees, pile their leaves as thick as you can on the bed when the veggies are finished this year. Remove them next spring before planting, or nothing else will grow either.

    Bookmark   August 5, 2011 at 2:40PM
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As an aside, I decided to skip removing the grass as I made a flower bed, and I put down pretty thick cardboard and several inches of leaf mulch on top of that. The only thing coming up is the Bermuda grass--it finds the gaps where the cardboard overlaps. It's been fairly easy to pull, but I hope I won't regret just digging up the lawn.

    Bookmark   August 5, 2011 at 2:53PM
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FADiver: I have the same problem with the grass growing in my raised beds. I've been pulling the grass as it emerges and keeping up with it so far. Next month, I plan to add 2 more raised beds to my garden - 3' x 6' ones. These will hold next spring's crop of strawberries and rhubarb. I do plan to implement suggestions from this thread: cardboard, newspaper, leaves, etc. I usually place the raised beds on areas of grass that aren't doing too well or devoid of grass altogether. Good luck to all of us with this problem!

    Bookmark   August 5, 2011 at 3:57PM
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nygardener(z6 New York)

Let me just add a thought: it's not that difficult to strip sod. Dig it up in chunks about 6-8" square. Whack as much soil as you can back into the bed, then compost the grass and roots. You could easily prepare a couple of 3' x 6' beds in an afternoon. Fork the soil underneath (optional), let it rest a couple of days, then erect your raised frame, fill it with soil, and you're ready to plant.

    Bookmark   August 5, 2011 at 5:22PM
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Just to be sure, are you sure it isn't seeds from the straw you are using. I purchased "straw" from my local nursery and it had many seed heads in it. They all seemed to find a way to sprout...or at least it felt like it. Good news is that they were really easy to pull up whenever I was near the raised bed.

If the grass is more than you can just pull out, I would consider emptying the bed and laying down an overlapping layer of cardboard or several layers of newspaper. Wet it and refill the bed. I used the newspaper method for all 5 of my raised beds and never had a problem with grass or weeds. I didn't go through the work of removing the sod first. Just plopped the bed on the ground, moistened (so it didn't shift when refilling) some newspaper on the bottom and partway up the sides, filled, and planted.


Here is a link that might be useful: My Garden

    Bookmark   August 5, 2011 at 5:29PM
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I've tried composting sod. In less than a year, I was pulling out the grass that had sprouted from the composty grave.

I don't compost anything anymore that has roots or might have lurking seeds.

    Bookmark   August 5, 2011 at 5:57PM
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dancinglemons(7B VA)

DH put in 3 raised beds for me 3 years ago. This is our third year and only minimal Bermuda grass coming through. Here is what he did.

1. Scalp the ground with the weed wacker down to dirt.
2. Lay down two layers of 10 year black weed blocker paper (water permeable). The bottom layer north to south and top layer east to west -and- he extended the paper about 3 inches outside the wood box.
3. Fill the beds (all 4x4) with potting mix and peat moss and all the old growing medium from our EarthBoxes.
4. During the summer and fall he regularly weed-wacks all around the raised beds to keep down any weeds in the area. The Bermuda grass has only rarely grown up thru the 10 inches of 'dirt' and I have no mulch around my okra, beans and squash. I plant collard greens in these same beds in fall and they stay until spring - still very, very few weeds.

I credit the scalping DH does with weed-wacker for keeping the weeds from growing wild around the beds. I credit the weed-block paper for keeping the weeds almost completely out of the beds.


    Bookmark   August 6, 2011 at 3:30AM
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ediej1209(5 N Central OH)

We put in a new raised bed this year and to help keep weeds out we put down cardboard followed by landscape fabric held down with those long pins, and piled with a couple of inches of wood mulch a foot outside the beds in all directions. Easier to walk on and I think I've maybe pulled a dozen weeds altogether from the raised bed so far this year. And like dancinglemons, we "scalped" the area before we put the cardboard down. Of course, we aren't dealing with bermuda grass, so I'm not sure how much that would work against something that invasive. Good luck!

    Bookmark   August 6, 2011 at 9:47AM
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I too have not dealt with bermuda, but let me mention that, after scalping the paths around the bed, you could put down old carpet, down face up (it will look much better). This will almost eliminate weed problems in the paths (a tiny fraction will actually push though carpet), and future weedwhackings. Do not put wood chips on the carpet, they will decay, make good soil, and weed seeds will blow in.

In regard to bermuda, I too think this is time for Roundup (next April, now it would not be effective). It will delay your planting some, and you will not kill it all. I would go black plastic early in season (to warm soil and speed up the process), heavy spray, heavy mulch, plant through mulch. Be prepared to apply it manually to isolated survivors with the help of a small paint brush. I have done the latter many times, without incident, and it is the best method for finishing the weeding of a bed.

    Bookmark   August 6, 2011 at 10:33AM
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dan_staley(5b/SS 2b AHS 6-7)

All these stories about cardboard and carpet won't do a thing for Bermuda. The runners will sit around in the dark for a year and wait for an opening. Srsly. Exclusion and killing will have to be done ongoing. I like what DancingLemons' DH did with the exclusion part.

Literally dozens of threads on this board with discussions. Maybe scores of threads, very common question here.


    Bookmark   August 6, 2011 at 11:34AM
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old carpet is fairly permanent. My FIL has had it in his paths for 30+ yrs. I have had it for 10+ yrs. There were less than ten breakthroughs through the carpet (many more at the cracks), all dealt with paint brush and Roundup, and all in the first year. You have to keep it clean of debris, or else new soil will accumulate, and roots will find openings much more easily from the top.

It is possible that laying the furry part down makes it much more difficult for rhizomes to find those openings (small holes in the base netting which is now at the top), the matted part at the bottom encouraging rhizomes to propagate horizontally. but should bermuda find thousands of openings, one pass with a larger paint brush will get them all for good.

    Bookmark   August 6, 2011 at 2:50PM
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Glib do you use Roundup full strength or diluted? I filled a roll-on bottle with dilute roundup to apply to bindweed leaves, it does not seem to be strong enough.

    Bookmark   August 6, 2011 at 4:50PM
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I use it full strength, and a small paint brush which I keep separated from the squash sex toys. For most weeds, painting one leaf is enough. The weed most resistant to RU is aronia (an understory tree with plentiful berries broadcast by birds) here. I have very little bindweed, surely I painted one at some point, but I can not remember.

    Bookmark   August 6, 2011 at 4:57PM
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